An image-conducting optical fiber bundle extends along a central bundle axis between image input and image output ends. The bundle is twisted along a portion of its length such that an image inputted into the image input end is angularly displaced about the central bundle axis before being outputted through the image output end. Each constituent optical fiber includes a cladding with a cladding diameter corresponding with the fiber diameter of that fiber and a core with a core diameter. The ratio of the core diameter to the cladding diameter defines a core-to-clad diameter ratio relative to each fiber. In various embodiments, at least one of fiber diameter and core-to-clad diameter ratio varies as a function of a fiber's radial displacement from the central bundle axis.
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1. A rigid image-conducting optical fiber bundle extending longitudinally along a central bundle axis between an image input end and an image output end and being twisted about the central bundle axis along a portion of its length such that an image inputted into the image input end is angularly displaced about the central bundle axis before being outputted through the image output end, the bundle comprising:
a plurality of adjacently fused constituent optical fibers, each optical fiber having a first end coinciding with the image input end and a second end coinciding with the image output end, wherein, as viewed into a selected cross-section of the optical fiber bundle
(i) each constituent optical fiber includes a cladding with a cladding diameter corresponding with the fiber diameter of that optical fiber and a core with a core diameter, and the ratio of the core diameter to the cladding diameter defines a core-to-clad diameter ratio relative to that optical fiber;
(ii) the bundle includes a plurality of at least two fiber zones including a at least a first fiber zone and a second fiber zone, the first and second fiber zones being concentrically arranged about the central bundle axis and defined such that the first fiber zone is nearer the central bundle axis than is the second fiber zone;
(iii) each fiber zone is populated by a plurality of optical fibers configured in accordance with a uniform specification relative to at least one of fiber diameter and core-to-clad ratio; and
(iv) among the fiber zones, at least one of
(a) the zone dependent fiber diameters of the constituent optical fibers increase as a function of radial displacement from the central bundle axis; and
(b) the zone dependent core-to-clad diameter ratios of the constituent optical fibers decrease as a function of radial displacement from the central bundle axis.
2. The optical fiber bundle of
3. The optical fiber bundle of
4. The optical fiber bundle of
5. The optical fiber bundle of
6. The optical fiber bundle of
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Priority based on two previous provisional applications is claimed. The first is Provisional Application Ser. No. 62/281,168 filed Jan. 20, 2016 under the title FOVEAL IMAGE INVERTER, while the second is Provisional Application Ser. No. 62/441,491 filed Jan. 2, 2017, also filed under the title FOVEAL IMAGE INVERTER. Moreover, the entirety of the previous provisional applications, including the drawings, is incorporated herein by reference as if set forth fully in the present application.
The transmission of images and, more generally, electromagnetic waves, through bundles comprised of adjacently fused optical fibers is an established art. Image conduits such as inverters (i.e., image inverters), tapers and “straight-throughs” are well known to practitioners of the fiber optic arts. Fused optical fiber image conduits find broad application as components in such devices as night visions goggles, rifle scopes, x-ray detectors and medical imaging apparatuses, by way of non-limiting example.
The basic fabrication techniques of each of the examples listed above have process steps in common. For instance, the most basic of fused optical fiber image conduits is a one-to-one, linear conduit having an input (e.g., image receiving) end and an output (e.g., image emitting) end. Light reflected from an object adjacent the input end enters the input end as an image. The image is conducted through the conduit and exits the output end from which a detector device or human eye senses it. In a simple one-to-one conduit, the image exits the output end without intentional alteration. For instance, the image is not magnified, reduced or angularly displaced about the longitudinal axis of the conduit.
Referring to
It will be readily appreciated that, as the heated bundle is twisted to angularly displace about the longitudinal axis of the conduit one end with respect to the opposite end, constituent fibers within the bundle are stretched lengthwise. Moreover, fibers that are more toward the periphery of the bundle are stretched to a greater extent than fibers that are more centrally located. As a result, fibers more toward the periphery decrease in diameter more dramatically than do fibers more toward the center, particularly in central regions along their lengths. Because, according to traditional fabrication methods, the constituent fibers of the bundle are all of the same cross-sectional dimensions, peripheral fibers are sometimes stretched and constricted to such an extent that their ability to transmit light efficiently is negatively impacted, which results in undesired image effects, including vignetting. One way of avoiding image-degrading constriction of peripheral fibers is to twist the bundle the desired number of angular degrees over a longer bundle length. However, this results in bundles that may be too long, heavy and unwieldy for use in the intended environment or application.
Accordingly, a need exists for a fused fiber bundle and method of forming an inverter from the same that facilitates image inversion over a relatively short bundle length while obviating the undesired peripheral image degradation associated with previous fused-bundle image inverters.
An illustrative embodiment of an imaging-conducting optical fiber bundle extends longitudinally along a central bundle axis between an image input end and an image output end. Between the opposed image input and output ends there extends a plurality of mutually and adjacently fused constituent optical fibers. Each constituent optical fiber has a first end coinciding with the image input end and a second end coinciding with the image output end. In various embodiments, each constituent optical fiber is configured as an imaging fiber capable of conveying an infinitesimal portion of an input image from the between the image input and image output ends. Moreover, the optical fiber bundle is twisted about the central bundle axis and along a portion of its length such that an image inputted into the image input end is angularly displaced about the central bundle axis before being outputted through the image output end.
In keeping with general convention, each constituent optical fiber includes an optically transmissive core about which there is collapsed and fused an optical cladding, the core and cladding having relative indices of refractive that facilitate propagation of electromagnetic waves through the core by means of total internal reflection. The cladding is defined by a cladding diameter that corresponds with the fiber diameter, while the core is defined by a core diameter. The ratio of the core diameter to the cladding diameter defines a core-to-clad diameter ratio relative to each fiber.
In some versions, the fiber diameters of the constituent optical fibers increase as a function of radial displacement from the central bundle axis. That is, as viewed into a selected cross-section of the bundle taken orthogonally to the central bundle axis, optical fibers more toward the outer boundary of the bundle have larger fiber diameters than do optical fibers more toward the central bundle axis.
In each of some alternative embodiments, the core-to-clad diameter ratios of the constituent optical fibers vary as a function of radial displacement from the central bundle axis. That is, optical fibers nearer the central bundle axis exhibit core-to-clad diameter ratios disparate by design from the core-to-clad diameter ratios of optical fibers situated more radially distant from the central bundle axis. In at least one version, as viewed into a cross-section of the bundle taken orthogonally to the central bundle axis, the core-to-clad diameter ratios of the plural constituent optical fibers are configured to decrease as a function of radial displacement from the central bundle axis. In still more specific alternative versions in which core-to-clad diameter ratios vary as a function of radial position relative to the central bundle axis, the fiber diameters of the constituent optical fibers may be configured, in one case, to remain constant as a function of radial displacement from the central bundle axis and, in another case, to vary as a function of radial displacement from the central bundle axis.
Representative embodiments are more completely described and depicted in the following detailed description and the accompanying drawings.
The following description of variously embodied foveal image inverters and methods of fabricating the same is demonstrative in nature and is not intended to limit the invention or its application of uses. Accordingly, the various implementations, aspects, versions and embodiments described in the summary and detailed description are in the nature of non-limiting examples falling within the scope of the appended claims and do not serve to define the maximum scope of the claims.
Many of the steps relative to the fabrication of a standard fused optical fiber bundle, including the special case of a fused-bundle image inverter, are applicable to the fabrication of optical fiber bundles and image inverters within the scope and contemplation of the present invention. These steps were summarized in the background with conjunctive reference to
Shown schematically in
In various aspects, the core 22 and the cladding 24 comprise optically-transmissive materials of differing indices of refraction, thereby facilitating internal reflection, as is known in the art. In alternative versions, at least one of the core 22 and cladding 24 comprises a glass. However, within the scope and contemplation of the invention are embodiments in which at least one of the core 22 and cladding 24 comprises a polymeric material (e.g., a plastic). In alternative variations in which at least one of the core 22 and cladding 24 is fabricated from a polymer, the cladding 24 and core 22 of each optical fiber 20 may be mutually joined or “fused” by, for example, heat fusion, as is typical of glass fibers, or by an alternative means such as an optical epoxy. Similar alternative methods may be used to join plural optical fibers 20 within the optical fiber bundle 10 to one another. In still additional versions, optical fibers 20 each of which comprises as least one of a glass and a polymer, may be retained in their respective positions within the overall optical fiber bundle 10 by a matrix 30 independent of the material from which the claddings 24 are formed. The matrix 30 could comprise, by way of example, a polymer, glass and/or optical epoxy.
Because a schematic cross-section is under consideration, it will be readily understood that the optical fiber bundle 10 could be either a straight-thru or an image inverter since planar cross-sections of these types of fused bundles could be indistinguishable. Moreover, while the constituent optical fibers 20 of the optical fiber bundle 10 in
Representative of the inventive concept is the inclusion with the optical fiber bundle 10 of a plurality of fiber zones Z1 through Zx concentrically arranged about the central bundle axis ACB, wherein Z1 is the fiber zone located closest to and/or including the central bundle axis ACB and Zx is the “outermost” fiber zone (i.e, the fiber zone radially most distant from the central bundle axis ACB). Moreover, the fiber zones Z1 through Zx are populated by optical fibers 20, the fiber diameters DF of which are zone dependent. More specifically, the average overall fiber diameter DF of constituent optical fibers 20 within the first fiber zone Z1 is smaller than the average overall fiber diameter DF of constituent optical fibers 20 within each fiber zone more radially distant from the ACB. More generally, the average overall fiber diameter DF of the optical fibers 20 within each fiber zone is greater (larger) than the average overall fiber diameter DF of the optical fibers 20 within each fiber zone closer to the central bundle axis ACB and less (smaller) than the average overall fiber diameter DF of the optical fibers 20 within each fiber zone more radially distant from the central bundle axis ACB.
By way of concrete non-limiting example, the illustrative optical fiber bundle 10 of
Referring still to the cross-sectional view of
Another way of conceptualizing the core-to-clad diameter ratio RCC is in terms of the cross-sectional area of a constituent optical fiber 20 that each of the core 22 and cladding 24 of the same represents. For example, consider first and second optical fibers 20 with the same cladding diameter Dclad. If the first optical fiber 20 has a core diameter Dcore that is smaller than the core diameter Dcore of the second optical fiber 20, then the first optical fiber 20 has a smaller core-to-clad diameter ratio RCC than the second optical fiber 20. Expressed in alternative terms, for an optical fiber 20 of a given cladding diameter Dclad, an increase in the core diameter Dcore corresponds to the core 22 representing an increased percentage of the overall cross-sectional area of the optical fiber 20 and the cladding 24 representing a correspondingly decreased percentage of the cross-sectional area of the optical fiber 20.
Relative to the formation of an optical fiber bundle 10 in which the output image is angularly displaced relative to the input image, it will be appreciated that an arrangement of optical fibers 20 to form a fiber bundle 10 such as that in
In accordance with an alternative configuration, fiber diameter DF is held constant among and across fiber zones Z1 through Zx, while the core-to-clad diameter ratio RCC varies as a function of fiber zone Z. In one version, an innermost first fiber zone Z1 comprises optical fibers 20 with a relatively high core-to-clad diameter ratio RCC, an outermost third fiber zone Z3 with a relatively low core-to-clad diameter ratio RCC, and at one intermediate second fiber zone Z2 situation between the innermost and outermost fiber zones Z1 and Z3 and comprising optical fibers 20 with a core-to-clad diameter ratio RCC between the core-to-clad diameter ratios RCC of the first and third fiber zones Z1 and Z3. In some such versions, the optical fibers 20 within each fiber zone Z are configured in accordance with a uniform specification to have the same core-to-clad diameter ratio RCC throughout the zone Z. However, in other variants, there is a mix within at least one fiber zone Z of optical fibers 20 having disparate core core-to-clad diameter ratios RCC. Examples of two alternative configurations of bundles 10 having variable core core-to-clad diameter ratios RCC across fiber zones Z are discussed in further detail below with conjunctive reference to the schematically-represented bundle cross-sections shown in
Referring now to
With reference to
A key difference between the examples of
Whether or not the second fiber zone Z2 of any particular embodiment includes fibers 20 of a second core-to-clad diameter ratio RCC2 unique to the second fiber zone Z2, the inclusion within the second fiber zone Z2 of a mixture of optical fibers 20 exhibiting both the first and third core-to-clad diameter ratio RCC1 and RCC3 results in a smoother, less obvious transition between fibers 20 of the first and third fiber zones Z1 and Z3. Optical fibers 20 of disparate core-to-clad diameter ratio RCC may be randomly distributed in the second fiber zone Z2 or well ordered. In at least one configuration, the inclusion within the second fiber zone Z2 of optical fibers 20 of the first core-to-clad diameter ratio RCC1 is more dense nearer the first fiber zone Z1, while the inclusion in the second fiber zone Z2 of optical fibers 20 of the third core-to-clad diameter ratio RCC3 is more dense nearer the third fiber zone Z3 thereby defining a sort of radially-dependent inclusion gradient of disparate core-to-clad diameter ratios RCC within the bundle 10. In addition to avoiding visible “steps” between fiber zones Z, the inclusion of optical fibers 20 of disparate core-to-clad diameter ratio RCC in different concentrations across the cross-section of the bundle 10 in accordance with a radial gradient mitigates structural stresses associated with the heating, drawings and twisting steps, and with the differing effects of thermal expansion on disparate fiber types.
Because variances in core-to-clad diameter ratios RCC even within each fiber zone Z are envisioned, it may be useful to conceptualize the core-to-clad diameter ratio RCC within any particular fiber zone Z as representative of an average core-to-clad diameter ratio RCC applicable to that zone, and the averages among all fiber zones Z as decreasing with radial displacement from the central bundle axis ACB. In accordance with this conceptualization,
Beyond the preceding, it is to be understood that, within any given configuration, variances in overall fiber diameter DF and core-to-clad diameter ratios RCC are not mutually exclusive. More specifically, while the description up to the present has considered alternative configurations in which, on the one hand, fiber diameter DF varies as a function of radial displacement from the central bundle axis ACB while core-to-clad diameter ratio RCC is constant across the bundle 10 and, on the other hand, fiber diameter DF is constant across the bundle 10 while core-to-clad diameter ratio RCC varies as a function of radial displacement from the central bundle axis ACB, expressly within the scope and contemplation of the invention are bundle configurations in which both fiber diameter DF and core-to-clad diameter ratio RCC varies as a function of radial displacement from the central bundle axis ACB.
The foregoing is considered to be illustrative of the principles of the invention. Furthermore, since modifications and changes to various aspects and implementations will occur to those skilled in the art without departing from the scope and spirit of the invention, it is to be understood that the foregoing does not limit the invention as expressed in the appended claims to the exact constructions, implementations and versions shown and described.
Higby, Paige, Tabor, Kevin, Onorato, Paulette I. K.
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Feb 14 2019 | ONORATO, PAULETTE I K | SCHOTT CORPORATION, INC | ASSIGNMENT OF ASSIGNORS INTEREST SEE DOCUMENT FOR DETAILS | 048357 | /0101 |
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